The present invention relates to an apparatus and method for acoustically guiding, positioning, and monitoring a tube or catheter within a body. More particularly, the present invention relates to an apparatus and method to guide the placement of a tube in a body conduit or cavity, to monitor the position of the tube, and to insure the patency of the tube in the body using a noninvasive acoustic technique.
Endotracheal tubes (hereinafter xe2x80x9cETTsxe2x80x9d), often referred to as breathing tubes, are used to provide a conduit for mechanical ventilation of patients with respiratory or related problems. An ETT is inserted through the mouth or nose and into the trachea of a patient for several reasons: (1) to establish and maintain an open airway; (2) to permit positive pressure ventilation which cannot be done effectively by mask for more than brief periods; (3) to seal off the digestive tract from the trachea thereby preventing inspiration of forced air into the stomach; and (4) as an anesthesia delivery system.
ETTs are used extensively in the field, emergency rooms, surgical suites, and intensive care units for patients that require ventilatory assistance. During intubation, an ETT is typically inserted into the mouth, past the vocal cords, and into the trachea. The proper location of the ETT tip is roughly in the mid-trachea. However, there are at least three possible undesired placement positions that can result, either during intubation or due to a subsequent dislodgment. One of these positions is in the esophagus. Another undesired position occurs from over-advancement of the ETT past the bifurcation of the trachea (carina) and into one of the mainstem bronchi. A third is above the vocal cords in the vocal tract.
The structure of the human airways is extremely complex. At the upper end of the trachea is the larynx containing the vocal folds, and at the lower end is the first bifurcation, known as the carina. The adult trachea is approximately 1.4 to 1.6 cm in diameter and 9 to 15 cm long. The newborn trachea averages about 0.5 cm in diameter and 4 cm in length. The airways that are formed by the carina are the right primary bronchus and the left primary bronchus. The right primary bronchus is shorter, wider, and more vertical than the left primary bronchus. For this reason a majority of erroneous ETT insertions past the carina tend to follow the right primary bronchus. Continuing farther down the airways, the bronchi branch into smaller and smaller tubes. They finally terminate into alveoli, small airfilled sacs where oxygen-carbon dioxide gas exchange takes place.
Providing a correctly positioned and unobstructed endotracheal tube is a major clinical concern. Any misplacement or obstruction of an ETT can pose a threat to the patient""s health. Misdirecting the ETT into the esophagus or locating the tip where there is a significant obstruction of its lumen can result in poor ventilation of the patient and eventually lead to cardiac arrest, brain damage or even death. Further, if the ETT is misplaced into a mainstem bronchus, lung rupture can occur.
If an ETT is obstructed with secretions or debris, a procedure known as endotracheal suctioning must be performed to clear the ETT. This procedure consists of introducing a sterile catheter through the ETT into the trachea, and applying negative pressure as the catheter is withdrawn. It has been estimated that this procedure is performed in Neonatal Intensive Care Units around 22,000 times per day in the U.S., and in many cases, it is performed as a preventive measure. Even though this procedure is performed very frequently, there are infrequent complications associated with its practice. These complications include hypoxia, bradycardia, tissue trauma, increase intracranial pressure, and tracheal or pharyngeal perforation.
In an attempt to avoid possible complications with ETT use, several techniques have been developed to aid clinicians in the proper placement/location of ETTs. Guidelines for the ideal technique are as follows: (1) the technique should work as well for difficult intubations as it does for those not so difficult; (2) the technique should indicate a proper ETT tip location unequivocally; (3) esophageal intubation must always be detected; and (4) clinicians must understand the technique and how to use it. The known techniques for clinical evaluation of ETT location include direct visualization of the ETT placement, chest radiography, observation of symmetric chest movements, auscultation of breath sounds, reservoir bag compliance, the use of a video stethoscope, fiberoptic bronchoscopy, pulse oximetry, and capnometry. However, none of the listed techniques allow a health care provider to constantly monitor the precise location of an ETT within the trachea, or the degree of obstruction of its lumen.
Apparatuses and methods for acoustically guiding, positioning, and monitoring tubes within a body are known in the art. See, for example, U.S. Pat. No. 5,445,144 to Wodicka et al., incorporated herein by reference, which discloses an apparatus and method for acoustically monitoring the position of a tube within a body conduit. In a preferred embodiment, a sound pulse is introduced into a wave guide and is recorded as it passes by a microphone located in the wave guide wall. After propagating down the ETT, the sound pulse is emitted through the distal tip of the ETT into the airway (or wherever in the body the tip of the ETT is located) and an acoustic reflection propagates back up to the wave guide for measurement by the same microphone. An absorptive material is located at the end of the wave guide to prevent further reflections of the sound pulse. The amplitude and the polarity of the incident and reflected sound pulse are used to estimate the characteristics of the airway at the tip of the ETT, and thereby guide the ETT placement or monitor the ETT for patency. In one preferred embodiment, a valve movable between a first and second position was included to provide communication between a mechanical ventilator and the proximal end of the ETT in the first position, and to provide communication between the wave guide and the proximal end of the ETT in the second position. Therefore, it is necessary during acoustical monitoring operations using the Wodicka et al. device to temporarily disconnect the mechanical ventilator (by switching valve positions) from the ETT.
As disclosed by Wodicka, et al., the acoustical properties of the airways of a respiratory system change dramatically over the audible frequency range. At very low frequencies, the large airway walls are yielding and significant wall motion occurs in response to intra-airway sound. In this frequency range, the airways cannot be represented accurately as rigid conduits and their overall response to sonic pulses is predictably complex. At very high audible frequencies, the large airway walls are effectively more rigid due to their inherent mass. However, one-dimensional sound propagation down each airway segment cannot be ensured as the sonic wavelengths approach in size the diameter of the segment, and effects of airway branching are thought to increase in importance. There appears to be a finite range of frequencies between roughly 500 and 6,000 Hz where the large airways behave as nearly rigid conduits and the acoustical effects of the individual branching segments are not dominant. It is over this limited frequency range where the complicated branching network can be approximately represented as a flanged xe2x80x9chornxe2x80x9d and where its composite acoustical properties reflect the total cross-sectional area of the airways.
The method and apparatus of the present invention distinguish between esophageal, tracheal, and bronchial intubations; are sensitive to small movements of the ETT; are able to continuously monitor the position of the distal tip of the ETT; and are not invasive. Furthermore, the apparatus of the present invention has no moving parts, and can be easily understood and operated by skilled clinicians.
According to one aspect of the present invention, an apparatus is provided for acoustically detecting the location of a distal end of a tube relative to a body conduit into which the tube is being inserted. The tube has a proximal end, and a distal end formed for insertion into the body conduit. The apparatus includes a speaker for generating a sound pulse in the tube; a first microphone for detecting a sound pulse in the tube at a distal position relative to the speaker, and for generating a first signal corresponding to the detected sound pulse; a second microphone for detecting a sound pulse at a position in the tube between the first microphone and the speaker, and for generating a second signal corresponding to a detected sound pulse; and a processor configured to receive the first and second signals and to discriminate between a distally traveling sound pulse and a proximally traveling sound pulse, the processor using the first or second signal generated from detection of the proximally traveling sound pulse to determine and report the location of the distal end of the tube relative to the body conduit.
In one embodiment of the invention, the processor is further configured to detect either a total or partial blockage in the tube. The processor can also be configured to detect a kink in the tube.
In another embodiment of the invention, the processor provides a signal representing the dimensions of the body conduit adjacent the distal end of the tube. In this embodiment, the invention can further include a warning signal generator for signaling when the dimensions signaled by the processor are not within a predetermined range. Furthermore, the warning signal generator can signal when the distal end of the tube moves relative to the body conduit.
In one embodiment of the invention, the tube is adapted to be coupled to a medical device, such as a mechanical ventilator, a breathing bag, an anesthesia machine, or an infusion pump. In a further embodiment, a display can be provided in electronic communication with the processor. The display can be designed to provide an indication of the dimensions of the body conduit adjacent the distal end of the tube, an indication of the patency of the tube, or an indication of the location of the distal end of the tube relative to the body conduit.
In another embodiment of the invention, there is provided an apparatus for acoustically detecting the location of a distal end of a tube relative to a body into which the tube is being inserted. The apparatus includes a sound pulse generator, a sound pulse receiver for signaling the detection of a sound pulse, a position indicator configured to report the location of the distal end of the tube relative to the body using the signal from the sound pulse receiver, and means for discriminating between a sound pulse traveling away from the distal end of the tube and a sound pulse traveling toward the distal end of the tube. In this embodiment, the sound pulse receiver is, for example, a first microphone and a second microphone, or a directionally sensitive microphone. The sound pulse receiver can be located at a distal position relative to the sound pulse generator, or at a proximal location relative to the sound pulse generator. In one aspect of this embodiment, the position indicator can also report whether the tube is obstructed. In another aspect, the position indicator provides an estimate of dimensions of the body adjacent the distal end of the tube. In yet another aspect, a warning signal generator is provided for signaling when the dimensions estimated by the position indicator are not within a predetermined range. The warning signal generator can be further configured to signal when the distal end of the tube moves relative to the body.
In yet another embodiment of the invention, a method of acoustically detecting the location of a distal end of a tube relative to a body is provided. The method includes the steps of generating a sound pulse in the tube; detecting a sound pulse; determining the direction of travel of the detected sound pulse; and determining the position of the distal end of the tube relative to the body using the detected sound pulse when the detected sound pulse is determined to be traveling away from the distal end of the tube. In one aspect of this embodiment, the method further includes the step of determining whether the tube is obstructed. In another aspect, the invention further includes the step of determining whether the tube is kinked. In yet another aspect of this method, the position determining step can include estimating the dimensions of the body adjacent the distal end of the tube. The position determining step can include the step of comparing a first signal representing a sound pulse detected by a first microphone with a second signal representing a sound pulse detected by a second microphone.
In a further embodiment of the invention, an apparatus for acoustically detecting the location of a distal end of a gas or liquid filled tube within a body conduit includes a sound pulse generator coupled to the tube, a sound pulse receiver or receivers coupled to the tube at a distal position relative to the sound pulse generator, a position indicator configured to report the location of the distal end of the tube in the body conduit using signals from the sound pulse receiver or receivers, and means for differentiating between a sound pulse traveling away from the distal end of the tube and a sound pulse traveling toward the distal end of the tube.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.